The present invention relates to an electromagnetically reciprocating apparatus which is used as, for example a fluid pump.
Fundamental construction of one example of a conventional electromagnetically reciprocating apparatus, which is used as a fluid pump (compressor, vacuum pump), is shown in FIG. 1. The conventional apparatus comprises: electromagnet 100, which is consisted of iron core 100a and coil 100b and repeats magnetization and demagnetization for one cycle of AC current; piston assembly 102, which includes magnetic material member 102a to be drawn by magnetized electromagnet 100, and front and rear pistons 102b, 102c disposed before and behind magnetic material member 102; front and rear cylinders 104, 106 for supporting front and rear pistons 102b, 102c of piston assembly 102; and a compression elastic member, wherein that is compression coil spring 108, which is compressed by piston assembly 102 moved in a forward direction (movement in a rightward direction in FIG. 1) by magnetic action of electromagnet 100 and moves piston assembly 102 in a backward direction (movement in a leftward direction in FIG. 1) by elastic force when electromagnet 102 is demagnetized.
In the electromagnetically reciprocating apparatus of this kind, operation efficiency becomes maximum when a vibration system having piston assembly 102 and elastic member (coil spring 108) is reciprocated in a resonance state.
More specifically, piston assembly 102 is reciprocated in the resonance state and an amplitude of reciprocating movement thereof is maximum when the following equation (1) is satisfied. That is, maximum operation efficiency of the electromagnetically reciprocating apparatus can be obtained.                     F        =                              1                          2              ⁢                              xe2x80x83                            ⁢              π                                ⁢                                                    Ks                +                Kf                            M                                                          (        1        )            
where
F: the frequency of the commercial electric power source (the number of pluses of DC power source)
M: the mass of piston assembly 102
Kf: the spring constant of a gas sealed in a sealed space 104a formed in front cylinder 104 partitioned by front piston 104
Ks: the spring constant of coil spring 108 compressed by rear piston 102c 
In a case that the electromagnetically reciprocating apparatus is used in different areas in which the commercial AC current have different frequency Fa, Fb (for example, Fa greater than Fb) to each other, at first, value of the spring constant (Ks+Kfa) of coil spring 108 and a gas in sealed space 104a, and the mass (M) of piston assembly 102 are set up in order to satisfy the following equation (2) and then make piston assembly 102 reciprocate in maximum amplitude of vibration in the area of frequency Fa.                     Fa        =                              1                          2              ⁢                              xe2x80x83                            ⁢              π                                ⁢                                                    Ks                +                Kfa                            M                                                          (        2        )            
where:
Kfa: the spring constant of a gas in sealed space 104a when the frequency is Fa
Then, in a case that the electromagnetically reciprocating apparatus, in which the various values are set as disclosed above, is used in the area of another frequency Fb, the following equation (3) is introduced.                     Fb         greater than                               1                          2              ⁢              π                                ⁢                                                    Ks                +                Kfb                            M                                                          (        3        )            
where:
Kfb: the spring constant of a gas in sealed space 104a when the frequency is Fb
From the equation (3), it becomes clear that piston assembly 102 can not reciprocate in the resonance state because either the spring constant (Ks+Kfb) is too small or the mass (M) of piston assembly 102 is too big.
Therefore, in Japan which is divided into two areas having the frequency of 50 Hz and 60 Hz of the commercial electric power sources, in order to make the conventional apparatus of the kind obtain the most preferably resonance state in the different frequency areas, the piston weight and the spring constant of coil spring (the elastic member) 108 are changed. This cause troubles that a manufacturing of various kinds of vibration systems having resonance frequency which are consistent with various kinds of frequency of the commercial electric power sources, and an independent storage of various kinds of vibration systems are needed.
The present invention has been made in consideration of the above situation, and has as its object to provide an electromagnetically reciprocating apparatus which can easily adjust the resonance frequency of a vibration system consisted of the piston assembly and the compression elastic member, etc. without changing the piston weight and the spring constant, and can easily adjust the resonance frequency of the vibration system at a place in which the electromagnetically reciprocating apparatus is used.
The fundamental construction of the electromagnetically reciprocating apparatus 10 of this invention for dissolving the above stated problems is shown in FIG. 2. This electromagnetically reciprocating apparatus 10 comprises: electromagnet 12 which is consisted of iron core 12a and coil 12b and repeats magnetization and demagnetization for one cycle of AC current or for one pulse of DC current; piston assembly 14 which includes magnetic material member 14a to be drawn by magnetized electromagnet 12, and front and rear pistons 14b, 14c disposed before and behind magnetic material member 14a; frond and rear cylinders 16, 18 for supporting front and rear pistons 14b, 14c; and a compression elastic member, wherein that is compression coil spring 20, which is compressed by piston assembly 14 moved in a forward direction (movement in a rightward direction in FIG. 2) by magnetic action of electromagnet 12 and moves piston assembly 14 in a backward direction (movement in a leftward direction in FIG. 2) by elastic force when electromagnet 12 is demagnetized. An air hole 21 is mounted on rear cylinder 18 to communicate a sealed space partitioned in rear cylinder 18 by rear piston 14c of piston assembly 14 with the outside of rear cylinder 18, and valve means 22 is mounted on air hole 21 to adjust a resonance frequency of the vibration system having piston assembly 14 and compression coil spring 20.
In fluid working chamber 16a which is disposed in front cylinder 16 so as to be expanded and reduced its volume by the reciprocal movement of piston assembly 14, fluid suction valve 16c for sucking fluid into fluid working chamber 16a in a volume expansion process of fluid working chamber 16a, and fluid exhaust valve 16d for exhausting fluid from fluid working chamber 16a in a volume reduction process are mounted.
In electromagnetically reciprocating apparatus 10 constructed as described above, the adjustment of opening of valve means 22 causes a sympathetic vibration of piston assembly 14 by the different electric power sources having different frequency.
It is preferable that the valve means is formed on an end wall of a housing the inner space of which communicates with the atmosphere, one end of the air hole is open to the sealed space of the rear cylinder and the other end is open at the outer end face of end wall of housing, and the inner space of the housing is open on the outer end face of end wall of housing at a position near to the other end of the air hole. It is also preferable that the valve means comprises a cap-like valve casing hermetically mounted on the outer end face of end wall of housing so as to cause an end face opening of the inner space of the valve casing to cover the other end of the air hole and the opening of the inner space of the housing, and a valve body arranged in the inner space of the valve casing so as to be movable between a closed position where communication between the other end of the air hole and the opening of the inner space of the housing through the inner space of the valve casing is interrupted and an open position where communication between the other end of the air hole and the opening of the inner space of the housing through the inner space of the valve casing is allowed.
The valve means having the structure as described above can be easily assembled in or disassembled from the electromagnetically driven reciprocating apparatus so as to perform repair and inspection.
In the electromagnetically reciprocating apparatus of this invention constructed as described above, it is preferable that the valve body of the valve means is accommodated in the inner space of the valve casing so as to pivot about an axis extending along the axis of the rear cylinder and is movable between the open and closed positions upon pivotal movement thereof, and the valve body includes an operation pin extending from the inner space of the valve casing in a direction along the axis thereof and exposed on an outer surface of the valve casing.
This valve means is more compact and has better operability.
When the electromagnetically reciprocating apparatus of this invention is constructed as described above, it is preferable that the compression elastic member is a compression coil spring arranged in the rear cylinder. When the compression elastic member is arranged as described above, the electromagnetically reciprocating apparatus can be made more compact.
Therefore, an electromagnetically reciprocating compressor or vacuum pump of this kind, which can be used in Japan having two areas in which the frequencies of commercial electric power sources are 50 Hz and 60 Hz, produces a sympathetic vibration of the vibration system by DC current pulse or AC current, having frequency between 50 Hz and 60 Hz, when the following (1) to (4) steps are practiced in the following order.
(1) The weight (M) of piston assembly 14 and the spring constant (Ks) of coil spring 20 are set up to make piston assembly 14 sympathetically vibrate at 50 Hz (specific frequency).
(2) The volume of sealed space 18a in the rear side is set up to make a gas in sealed space 18a has a spring constant (Kr) which produces sympathetic vibration at 60 Hz (desired frequency).
(3) Air hole 21, having an enough opening area so as not to resist the sympathetic vibration at 50 Hz, is mounted on rear cylinder 18.
(4) Valve means 22 is mounted on air hole 21. After execution of the above steps (1) to (4), the vibration system can sympathetically vibrate either at 50 Hz or at 60 Hz by adjusting the opening of valve means 22.
In the electromagnetically reciprocating apparatus of this invention, the resonance frequency of vibration system can be adjusted by every easy operation. That is, the movement of piston assembly can be adjusted to make a maximum vibration (resonance frequency state), which is preferable in the usage of the apparatus in the areas having different frequency of AC current, by the only adjustment of valve means without the changing of piston weight and the spring constant to make the resonance frequency of vibration system be inconsistent with the frequency of supplied electric current.
Further, the possibility of adjustment described above produces a very superior technical advantages that a fluid pump of high performance is easily gained even if the piston weight and the spring contact have a slight variation.